Negative motor phenomena (lapses in normal muscle tone, manifested by prolonged silence on electromyography) are present in several pathological states and produce major motor disability in patients affected with these problems. Three major neurological disorders in which negative motor phenomena play a devastating role are cataplexy and certain forms of epilepsy and myoclonus. The treatments available for "positive" and typical forms of epilepsy and myoclonus rarely improve those patients in which negative motor phenomena are also present. Sudden loss of motor tone causes the patients to fall down, impair motor coordination, and interfere with activities of daily living. New advances in physiology make this an opportune time to review this entire subject. Asterixis is the most familiar form of negative myoclonus. The type of negative myoclonus affecting thigh muscles, as commonly occurs in patients with post-hypoxic action myoclonus, prevents ambulation. Atonic seizures, that occur in several types of epilepsy syndromes, such as the lennox- Gastaut syndrome. Cataplexy is a dramatic disorder triggered by an emotional stimulus, with the patient suddenly losing motor tone, falling down, and being unable to move. Negative motor phenomena occur in choreic disorders (being called motor impersistence) and account for the dropping of objects.The 'freezing' phenomenon in Parkinson's disease may be a negative motor phenomenon. All of these forms of negative motor phenomena have ben highly resistant to any form of treatment. Negative motor phenomena can appear in normal motor behavior, such as in REM sleep, and possible in silent periods in electromyography. The neural basis for loss of motor tone unknown, and to date, no formal scientific meeting devoted to negative motor phenomena has ever been held. In a three day workshop, invited discussants and participants will review the current state of knowledge in their field of expertise and present their research in those areas. The workshop will bring together neuroscientists and clinicians renowned for work in subspecialties relating to negative motor phenomena, including neurophysiology, neurochemistry, neuroanatomy, epileptology, sleep disorders and movement disorders. Normally, such individuals would not share the same scientific meetings, so this workshop will allow them to learn from one another. The material will encompass all that is known on the subject, and each participant will write a review chapter that will be part of a monograph which should serve as the definitive volume on negative motor phenomena. We hope to achieve a new level of understanding with the expected compilation of current knowledge and anticipate that new research strategies will emerge.